When a power supply of an external power system (referred to as a grid) decreases by an accident and the like or when a power demand seasonally increases, the power demand becomes larger relative to the power supply and an unexpected power interruption might occur. In addition, a temporary power interruption due to a torrential rain, lightning and the like is supposed, so that it is known that an uninterruptible power supply (UPS) to supply power to a computer and a peripheral device when power failure such as the power interruption occurs is used. However, a conventional uninterruptible power supply is effective only against a brief power interruption and this merely serves to temporarily supply the power to the computer and the peripheral device. Therefore, this is insufficient for supplying the power in a home when a large-scale and long-time power interruption occurs. Further, there is a problem that the uninterruptible power supply operates at the time of the power interruption and this cannot be used for decreasing power usage of the grid.
Recently, a larger-capacity home storage device is put into practical use. It is possible to secure the power supply at the time of the power interruption to decrease the power demand and the power usage of the external power system by using the home storage device. For example, it is considered to decrease the supply of AC power from the external power system to make up for power shortage by the storage device.
In a next-generation power grid (hereinafter, referred to as a smart grid), which solves a problem in power transmission between a supplier and a demander using information technology, control for cutting back power consumption of a demander side (DR (demand response)) may be performed by a supplier side. For example, during peak power demand periods, load control in which a power provider changes a preset temperature of a home air conditioner is performed. Measures including such DR taken by the supplier side to the demander side are referred to as DSM (demand side management).
Patent Document 1 discloses that power consumption of a plurality of equipment instruments connected to a home network is controlled by an overall control device, and each of a plurality of equipment instruments is provided with a secondary battery to be operated by power of the secondary battery during peak power periods and operated by power from a commercial power supply and charge the secondary battery during off-peak periods. The overall control device receives a power control instruction from the power supplier side.